Identify and construct intervals by number and quality, invert them, recognise them by ear, and transpose melodies for different keys and instruments.

What this dot point is asking

Measuring intervals: number and quality

To name an interval, first count the number. Count the letter names from the lower to the upper note inclusively, so C up to E spans C, D, E, which is a third. The number ignores sharps and flats; it only counts staff positions.

Then find the quality by counting semitones. The unison, fourth, fifth and octave can be perfect, augmented or diminished. The second, third, sixth and seventh can be major, minor, augmented or diminished. A major interval made one semitone smaller becomes minor; a minor made one smaller becomes diminished; a major or perfect made one semitone larger becomes augmented.

A reliable method is to treat the lower note as a tonic. Ask whether the upper note belongs to that major scale. If it does, the interval is major (for 2nd, 3rd, 6th, 7th) or perfect (for 4th, 5th, 8ve). If the upper note is a semitone lower than the scale degree, the interval is minor or diminished.

Common intervals to memorise

Some semitone counts are worth knowing instantly: minor second is 1 semitone, major second is 2, minor third is 3, major third is 4, perfect fourth is 5, tritone (augmented fourth or diminished fifth) is 6, perfect fifth is 7, minor sixth is 8, major sixth is 9, minor seventh is 10, major seventh is 11, octave is 12.

Inversion

Inverting an interval means moving the lower note up an octave (or the upper note down) so they swap positions. The numbers always add to nine: a third inverts to a sixth, a fourth to a fifth, a second to a seventh. Quality flips too: major becomes minor, minor becomes major, augmented becomes diminished and diminished becomes augmented, while perfect stays perfect. So a major third inverts to a minor sixth, and a perfect fifth inverts to a perfect fourth.

Hearing intervals

Aural tasks ask you to identify intervals by ear. The standard trick is to link each interval to the opening of a well-known tune. A perfect fifth opens many fanfares, a perfect fourth has a strong open sound, a minor third sounds slightly sad, and a major third sounds bright. The tritone is restless and unstable. Practise singing up and down from a given note so you can produce as well as recognise each interval, because the external exam tests both directions.

Transposition

Transposition rewrites music so every note moves by the same interval, preserving the melody's shape and intervals while changing its key. You transpose to suit a singer's range, to make reading easier, or to write for a transposing instrument.

There are two common reasons. To change key, decide the interval between old and new tonic, then move every note and rebuild the key signature. To write for a transposing instrument, remember that a written note sounds at a fixed interval away: a B flat clarinet sounds a major second lower than written, so to keep the same concert pitch you write its part a major second higher.

Putting it together

Interval work underpins almost everything else in the course: chords are stacks of intervals, transcription depends on hearing them, and transposition relies on applying one interval consistently. Drill number and quality until naming is automatic, learn the rule of nine for inversions, and rehearse aural recognition both up and down. For transposition, always rebuild the key signature rather than writing accidentals on every note.